Echo-ranging apparatus



Junev 1s, 196s Filed June 2l, 1966 W. HALLIDAY ET Al.

ECHO-HANGING APPARATUS 2 Sheets-Sheet 1 mfr'll, 641.1, *AHM-hey,

June 18, 1968 W. HALLIDAY ETAL ECHO-HANGING APPARATUS Filed June 2l,1966 2 Sheets-Sheet 2 WILL/AM Hmm/1y y FOY WILL/AM E0/wf /lnsLErr faceof a spherical, concave reflector 2 of rectangular aperture. Thetransducers 1, which are electrostrictive transducers are associatedrespectively with seventy separate transmission-reception channels 3,each transducer 1 being coupled to its respectively-associated channel 3via an electrical path 4. The channels 3 are each coupled via anindividual electrical path to a common transmission-control unit 6, andvia an individual electrical path 7 to a common display unit 8, the twounits 6 and 8 being interconnected via an electrical path 9. Electricalcarrier-wave oscillations are supplied to the seventy channels 3 via acommon electrical path 10 from the unit 6.

The transducers 1 and reflector 2 are mounted externally of the hull ofthe ship below the water surface, with each transducer 1 substantiallyupright and with the longer aperture-dimension of the reflector 2horizontal. Under control of the common transmission-control unit 6, thechannels 3 supply pulses of the carrier-wave oscillations via the paths4 to the transducers 1 to cause the transducers 1 to emit into thewater, and towards the reflector 2, corresponding pulses of acousticoscillations. These acoustic pulses are reflected from the reflector 2in a general direction inclined downwardly from the ship, the reector 2being tilted downwardly slightly with respect to the transducers 1 sothat the transducers 1 do not obstruct the reflected pulses. Eachindividual transducer 1, since it is situated on the focal surface ofthe reflector 2, acts together with the reflector 2 to produce a beam ofpulsed acoustic energy inclined downwardly in elevation. Since thetransducers 1 are closely positioned side-by-side around the focalsurface, the seventy transmitted beams are closely spaced angularly withrespect to one another in azimuth; the transducers 1 in combination withthe reector 2 thereby transmitting seventy separate beams of pulsedacoustic energy equally inclined downwardly in elevation, but fanningout from one another in different directions throughout a limitedazimuthal sector centered on the ship. If any of the transmittedacoustic energy is reflected back as an echo from one of thesedirections, then this refiected energy is accordingly directed by thereflector 2 to the particular transducer 1 giving rise to transmissionin that direction. Reception of an echo by any transducer 1 generatestherein an electric signal that is passed via the appropriate path 4 tothe associated channel 3. After amplification and detection, theelectric echo signal is passed via the relevant path 7 for display bythe display unit 8. Synchronisation of the time-base of the display withthe transmission of the acoustic pulses is achieved by means of anelectric signal supplied to the unit 8 via the lead 9 and coordinated inits timing with the supply of pulses from the channels 3 to thetransducers 1.

The use of the separate channels 3 in the reception of the echo signalsensures that the directional information relating to each echo ispreserved, the directional acuity being dependent upon the width of beamoriginating from each transducer 1 via the reflector 2, and also uponthe number of transducers 1 (and thereby the number of separate beamsused) for the sector covered. In the present example, each beam has ahalf-power width of 0.32 degree in the plane of the longeraperture-dimension of the reflector 2 and a half-power width of twodegrees in the plane of the shorter aperture-dimension, the seventybeams being distributed uniformly throughout a sector of thirty degrees.The wavelength of the acoustic energy in water is in this case 0.6centimetre and the reflector 2 has a focal length of fifty centimetreswith longer and shorter aperture-dimensions of ninety-five and fifteencentimetres respectively. (The width of the beam in degrees and measuredin the plane of either aperture-dimension is in the present caseapproximately 51A/X where A is the wavelength and X the relevantaperture-dimension.) Each transducer 1 has a length, measuredsubstantially parallel to the shorter aperture-dimension of thereflector 2, of 2.4 centimetres, and a width, measured substantiallyparallel to the longer aperture-dimension, of 0.38 centimetre.

The width, in particular, of each transducer 1 is chosen to be as smallas possible consistent with efficient operation, in order that a largenumber of transducers 1 can be accommodated side-by-side on the focalsurface to produce a correspondingly large number of beams within thesector, and thereby ensure a high degree of acuity. In this respect, thewidth is chosen by reference to the distribution of energy that obtainson the focal surface of a concave spherical reflector of circularaperture and illuminated with acoustic energy from infinity. To a largeextent the energy received in the latter case is concentrated in acentral circular region of the distribution pattern, the radius R ofthis circular region, the Airy disc, being related to the focal length Fand the diameter D of the aperture, and to the wavelength A, by theformula:

With the specific values of focal length (fifty centimetres) andwavelength (0.6 centimetre) quoted above in relation to FIGURE l, areflector having a circular aperture of diameter ninety-five centimetresgives rise to an Airy disc having a radius of 0.38 centimetre. Asubstantial part of the energy distributed within the Airy disc isconcentrated in the central area bounded by a circle of half thisradius, so that useful reception of the energy can accordingly be madeby a transducer extending across this central area alone, that is tosay, over a width of 0.38 centimetre. By analogy, useful reception ofenergy from the spherical reflector 2 of rectangular aperture, isachieved parallel to the longer aperture-dimension of ninety-fivecentimetres over a width of 0.38 centimetre in the focal surface, thatis to say, over the width chosen for each transducer 1. The transducers1 in this case are positioned side-by-side along an arc of the focalsurface extending through thirty degrees at a radius of fiftycentimetres; with a width of 0.38 centimetro each, seventy transducers 1are accordingly readily accommodated along this arc, to give efficientrecepion of echoes from seventy angularlyspaced directions within thesector of thirty degrees.

The length of each transducer 1 measured parallel to the shorteraperture-dimension of the reflector 2, is chosen as 2.4 centimetres on asimilar basis to choice of the width. Consideration is given in thisinstance to the Airy disc applicable to a concave, spherical refiectorhaving a circular aperture of fifteen centimetres, the radius R of thisdisc being 2.4 centimetres.

Considering the apparatus of FIGURE 1 in greater detail, eachtransmission-reception channel 3 includes a transmit-receive switch 11,and it is to this switch 11 that the associated transducer 1 is coupledvia the relevant path 4. A transmitter-amplifier 12 and areceiver-amplifier 13 are both connected to the switch 11 within thechannel 3, the switch 11 serving to isolate the amplifier 13 from pulsedelectric carrier-wave signals supplied by the amplifier 12 fortransmission to the transducer 1 via the path 4, and also to isolate theamplifier 12 from the path 4 while echo signals are being passed fromthe transducer 1 to the channel 3 via the path 4.. The pulsedcarrier-wave signals are supplied through the amplifier 12 from a gate14, the gate 14 receiving from the common transmissioncontrol unit 6 thesignals supplied to the channel 3 via the paths 5 and 10. The unit 6supplies a train of gating pulses to the lead 5, and these pulsescontrol operation of the gate 14 to pass to the amplifier 12corresponding pulses of the electric carrier-wave oscillations suppliedfrom the path 10. The carrier-wave oscillations in the resent examplehave a frequency of two-hundred-andfifty kilocycles per second, and eachpulse of oscillations has a duration of thirty microseconds.

During the intervals between successive pulses supplied to the path 4via the amplifier 12 and the switch 11, echo signals passed via the path4 to the channel 3 are passed through the switch 11 to the amplifier 13.The amplifier United States Patent O 3,389,372 ECHO-RANGING APPARATUSWilliam Halliday, London, and Roy William George Haslett, Ilford,England, assignors to Smiths Industries Limited, London, England, aBritish company Filed June 21, 1966, Ser. No. 559,292 13 Claims. (Cl.340-3) ABSTRACT OF THE DISCLOSURE A sonar system includes a side-by-sidearray of electromechanical transducers mounted on the focal surface of aspherical reflector to transmit and receive acoustic waves in respectivedirections throughout a sector of surveillance. Each transducer has itsown transmitting and receiving channels, and a display unit common to`the receiving channels displays each detected echo with adirectionality dependent upon which of the receiving channels detectedthat echo.

This invention relates to echo-ranging apparatus.

The invention is particularly, although not exclusively, concerned Withsonar apparatus, that is to say with echo- -ranging apparatus in whichacoustic wave energy Vlof frequency not necessarily within theaudibile-sound range) is propagated in, for example, the sea. Althoughof especial application to sonar apparatus using acoustic wave energy,the invention is also applicable to radar apparatus -usingelectromagnetic wave energy.

Surveillance of a defined angular sector in azimuth or elevation,Whether in water or space, is conventionally carried out 'by sweeping abeam of the appropriate acoustic or electromagnetic wave energy throughthe sector, the directions from which echoes are received during thesweep providing directional information as to the echoproducing bodies,the targets, Within the sector. Reception of the echoes with therequired degree of directional acuity is normally carried out using thesame transducer or aerial array as used for transmitting the beam ofwaves, the array having, by reciprocity, directionalbeam-characteristics for reception corresponding to those fortransmission. Various proposals have been made for sweeping atransmitted beam and its corresponding received beam through a sector ofsurveillance, but these involve either undesirable mechanical movementsor somewhat complicated electronic methods of varying the phasing withrespect to one another of a multiplicity of electric signals. Where apulsed beam of `Jvave energy is transmitted and the whole angular rangeof the sector is to ybe scanned within the duration of each pulse, thereiS the added disadvantage that the minimum duration of transmitted pulsethat can be used is limited by the maximum speed of beam-sweepingobtainable in those circumstances.

It is an object of the present invention to provide echorangingapparatus that can be used to avoid the above disadvantages.

According to the present invention echo-ranging apparatus comprises amultiplicity of echo-receiving elements arranged such that differentelements receive echoes from different directions throughout an angularsector, a multiplicity of reception channels coupled respectively tosaid elements for detecting echoes received by the elements, Iand meansfor providing a representation of at least the directions within saidsector from which echoes detected as aforesaid are received, therepresentation of direction of reception of each such echo beingprovided in accordance with whichever of the reception channels detectsthat echo.

With echo-ranging apparatus according to the inven- Crt rice

tion therefore, there is no requirement for mechanical or electronicscanning of the sector under surveillance (and accordingly there is nountoward limitation imposed by maximum speed of scanning), since theechoes from the different directions within the sector are received -bythe different echo-receiving elements. These elements may be mountedside-by-side on, or near, the focal surface of a concave reflector. Thereflector may be a spherical or cylindrical reflector ywith the elementsmounted as a singledimensional array, or, in the case 0f the sphericalreflector, as a two-dimensional array.

The echo-ranging apparatus may be sonar apparatus, `the echo-receivingelements being electromechanical transducers (for example,electrostrictive transducers of barium titanate) for receiving 'acousticechoes, and being mounted closely side-by-side to receive echoes fromdifferent closely-spaced angular directions throughout the sector. Whenused with a spherical or cylindrical concave reector, the minimumangular spacing that can be obtained between the directions of receptionis dependent to a substantial extent upon the closeness with which thetransducers can be accommodated side-by-side on the focal surface. Thesize of each transducer is in this respect preferably chosen to be assmall as usefully practicable with regard to the distribution in thefocal surface of echoenergy received from the relevant direction by thattransducer. The use of Ia small size enables a large number oftransducers to be accommodated to cover any particular angular sectorwith a high degree of directional acuity.

According to a feature of the present invention, sonal apparatuscomprises a concave spherical or cylindrical reflector, a multiplicityof electromechanical transducers mounted closely side-by-side -around anarc of the curved focal surface of the reflector for receiving via thereflector acoustic echoes from a multiplicity of closelyspaced angulardirections throughout a predetermined sector, different ones of saidtransducers receiving echoes as aforesaid from different ones of saiddirections, a multiplicity of reception channels coupled respectively tosaid transducers for detecting echoes received by the transducers, `anda display unit for providing a display of both direction and range fromwhich echoes detected as aforesaid are received, the representation ofdirection of reception of each displayed echo `being provided inaccordance with whichever of the reception channels detect that echo.

The closely-spaced directions of reception may be equallyangularly-spaced from one vanother throughout the sector.

The electromechanical transducers, as mentioned earlier, may `beelectrostrictive transducers, and may be, for example, of bariumtitanate.

Sonar apparatus in accordance with the present invention will now bedescribed, by Way of example, with reference to the accompanyingdrawings, in which:

FIGURE l is a schematic representation of the sonar apparatus, only oneof a multiplicity of transmissionreception channels of the apparatusbeing shown in detail;

FIGURE 2 is a block schematic representation of a display unit of thesonar apparatus shown in FIGURE 1;

FIGURE 3 illustrates an alternative form of the display unit; and

FIGURE 4 illustrates a further alternative form of the display unit.

The sonar apparatus is for use on a ship to receive acoustic echoes fromunderwater targets The targets may be tish or other underwater objectsspaced from, or on, the bottom, and the bottom may in itself be atarget.

Referring to FIGURE l, seventy identical and elongated electromechanicaltransducers 1 are mounted closely side-by-side around a portion of thespherical focal sur- 13, which has automatic gain control, amplies eachecho signal and passes this to a detector 15, the resultant, detectedsignal being supplied from the channel 3 to the common display unit 8via the relevant path 7.

The display unit 8 provides, in accordance with the signals it receivesvin the seventy paths 7, a display indicating both the direction andrange from which echoes are received by the apparatus. Signalsrepresenting echoes received from different bearings are received by theunit 8 via different ones of the paths 7, the particular path '7involved in each case signifying the relevent ection. The timing of thereceived echo in relation to the transmitted pulse provides, in theconventional manner, a measure of the range from which the echo isreceived. The actual construction of the display unit 8 is not ofprimary importance, but it can conveniently be as shown in FIGURE 2.

Referring to FIGURE 2, the display is provided by a cathode-ray tubeunit 17, the unit 17 being connected to the paths 7 one at a time and inturn through an electronic switch 18. The switch 18 receives, in commonwith a time-base unit 19, the synchronisation signal supplied via thepath 9 from the common transmission-control unit 6, and this serves tocoordinate the stepping sequence of the switch 18 with the time-base ofthe display. The time-base unit 19 supplies to the unit 17 time-basewaveforms appropriate to the representation in Cartesian coordinates ofrange against bearing, that is to say, appropriate to a Type B display.ln this display, the echoes are indicated by intensity modulation of thecathode-ray trace, all the paths 7 being connected to the time-sharedunit 17 in turn as the trace is swept progressively across thebearing-axis of the display. The full sweep of the trace, and hence thesampling of all seventy paths 7, takes place within the duration of atransmitted pulse, that is to say, all within thirty microseconds,

Where, from a practical standpoint it is desired to avoid the need for asampling switch such as the switch 18, a form of display unit 8 notinvolving time-sharing may be used. Alternative forms of the unit 8 notinvolving time-sharing are illustrated in FGURES 3 and 4.

Referring to FIGURE 3, the seventy paths 7 are connected respectively toseventy recording pens 20 that are carried together, but spaced from oneanother, across the width of a recording paper 21. The paper 21 movesslowly lengthwise under the pens 2) and is marked by them in accordancewith the echo signals received, the particular position in each vasebeing indicative, by its distance across and along the paper 21respectively, of the bearing and range from which the relevant echo isreceived. it may be arranged that the same length of paper 21 movesunder the pens 20 during repeated recording sequences so that therepresentations of corresponding echoes received during the successivesequences are correlated with one another in the record.

Referring to FIGURE 4, the seventy paths 7 ,are in this case connectedrespectively to seventy indicating lamps 22. The lamps 22 (which may be,for example, neon or gallium-arsenide lamps) are carried together, butspaced apart from one another, across the width of a rectangular displayarea 23. The lamps 22 are moved together from one end to the other alongthe length of the area 23, the lamps 22 emitting light in response tosignals supplied from the paths 7. The position across the width of thearea 23 and along its length at which light is emitted, indicates thebearing and range from which an echo is received.

The apparatus described above with reference to FIG- URE 1 providesconstant surveillance, with a high degree of acuity, throughout thedefined angular sector, and does this without the need for anymechanical or electronic method of repeatedly sweeping or scanning thesector with a narrow beam of acoustic energy. Accordingly, since thereis no limitation imposed by beamscanning speed, there is no untowardrestriction on the duration of transmitted pulse used. These advantagesare achieved simply and economically, the need to provide themultiplicity of separate transmission-reception channels 3 being readilymet using, for example, techniques involving printed-circuitconstruction. Clearly, the channels 3 could be simplified by arrangingthat the function of each is limited to reception, transmission beingcarried out by means of a unit common to all the transducers 1. Thiswould not necessarily lead to economy and more ecient operation, owingto the fact that the power required from the common transmission unitwould be some seventy times that required from each individual channel3. Additionally, there would be the need to effect very rapid switchingof connections to the transducers 1 between the periods of transmissionand reception. In order to avoid this switching, separate transducersfor transmission and reception could be used, transmission being made bya transducer not associated with the reflector 2.

With the separate transmission-reception channels 3, the transmission ofpulses from the different transducers 1 may be etected concurrently orsequentially, and ,may also be made conveniently using different carrierfrequencies as between these transducers 1. The use of diiferent carrierfrequencies in this manner can be practical importance in distinguishingbetween echoes received from the region where side-lobes of adjacenttransducers 1 overlap one another. The side-lobes of the transducers 1could be reduced by shaping the transducers 1 themselves, but the sameetiect might be achieved more readily by shaping of the reflector 2.

Simplification in the construction of the reliector 2 can be achievedusing a cylindrical rather than spherical, concave form. The aberrationintroduced if the spherical reliector 2 is replaced by a cylindricalreflector having its axis of curvature parallel to the shorteraperture-dimension, is dependent upon this dimension and the radius ofcurvature involved. Provided that the change in acoustic path-lengthintroduced at any point in the aperture is substantially less than aquarter of the relevant wavelength, the aberration for normal purposescan be eX- pected to be small.

With the sonar apparatus described with reference to FIGURE 1,directional acuity is obtained throughout a sector in one plane only. Ifdirectional acuity is required in both elevation and azimuth, then atwo-dimensional array of transducers rather than the one-dimensonalarray of FIGURE 1, can be used with a spherical reflector If a squarearray is used with a reflector of circular aperture, then the samedirectional acuity can be obtained in both planes. The echo signalsderived by the separate channels of the two-dimensional array may beused to provide a two-dimensional display picture of the water at aselected range, targets in the plane normal to the acoustic lbeams atthis range being represented in the display at positions correspondingto the positions in the plane. The acoustic signals transmitted in thiscase can be continuous wave (CW) instead of pulsed; it may be necessaryin certain cases `to increase the frequency of these signals in order toobtain the desired acuity.

Display techniques involving stereoscopic effects, real or simulated,may be employed with the apparatus. Additionally, by displacing thearray of transducers 1 slightly with respect to the reflector 2, therange at which targets are in focus can be selectively adjusted. Bysuitable choice of the parameters of the -array and reiiector 2, a smalldepth of field can be obtained, targets within focus being presented fordisplay with partial elimination of targets out of focus. A stop,positioned at the centre of curvature of the reilector 2, may be used tolimit the exitand entryangle of acoustic energy with respect to therecctor 2, and thereby ensure uniform acoustic illumination across theeffective aperture of the system.

The sonar apparatus described above with reference to FIGURE l mayclearly be used on the ship to provide either a forward or asideways-looking search. The plane of the sector of search may bevertical instead of horizontal as described, and in this case it may bearranged that each beam is inclined, downwardly, to the vertical. Adisplay limited to the bottom of the water and the region just above itcan in these circumstances be obtained simply by arranging that the unit8 displays in sequence the detected signals applied via the paths 7. Theearliest echo of the bottom received by the apparatus after transmissionof a pulse, is that originating from the beam of least inclination tothe vertical, so that by selecting the detected signal on the lead 7appropriate to this beam, and then the detected signals on the otherlead 7 in sequence thereafter, a display limited to the bottom and itsadjacent region of water over a substantial distance, can be achievedwith a high degree of acuity.

Although the apparatus of the present invention is referred to ingeneral terms as echo-ranging apparatus it is to be understood that inits broadest aspect the invention as described and claimed herein, doesnot necessarily involve measurement of range, the term echo-rangingbeing used simply to refer to the kind of apparatus in which sensing ofechoes is utilised.

We claim:

1. Echo-ranging apparatus comprising: means for receiving echoes from amultiplicity of different directions throughout a predetermined angularsector, said means comprising an echo-reflector having a concaveretiec-ting surface that is of circular arc in section, and amultiplicity of echo-receiving elements mounted side by side around thefocal surface of said reliector to receive echoes via said reectingsurface from respective ones of said directions, said elements beingmounted in a circular arc concentric With said arc of section; amultiplicity ot' reception channels coupled respectively to saidecho-receiving elements for detecting echoes received by said means; andfurther means coupled to said reception channels for providing arepresentation of at least the directions Within said sector from whichechoes detected as aforesaid are received, said further means providingrepresentation of direction of reception of each such echo in accordancewith whichever of the reception channels detects that echo.

2. Echo-ranging apparatus according to claim 1 wherein the reflector isa spherical concave reflector.

3. Echo-ranging apparatus according to claim 1 whereing said furthermeans includes means for displaying detected echoes each in accordancewith the direction and range from which that individual echo isreceived.

4. Echo-ranging apparatus according to claim 3 wherein said furthermeans comprises a display device and a switch for coupling the receptionchannels in turn to the display device to receive from the receptionchanneis sequentially signals in accordance with echoes detected by thedifferent reception channels.

5. Echo-ranging apparatus according to claim 3 including a multiplicityof echo-recording devices, und means coupling different ones of therecording devices to diiferent ones of the reception channels to recordechoes detected by the different channels.

6. Echo-ranging apparatus according to claim 5 including a recordingsurface, and a multiplicity of spaced pens for marking the recordingsurface in accordance with echoes detected by the different receptionchannels.

7. Echo-ranging apparatus according to claim 3 including a multiplicityof indicating devices, and means coupling different ones of saidindicating devices to different ones of the recept-ion channels toprovide indication of echoes detected by the different receptionchannels.

8. Echo-ranging apparatus according to claim 7 wherein the indicatingdevices are spaced lamps.

9. Echo-ranging apparatus according to claim 1 including a multiplicityof separate transmission channels coupled respect-ively to said elementsfor supplying electric carrier-wave oscillations thereto, each saidtransmission channel being individually actuable to supply saidcarrierwave oscillations to its respective one of said elements, eachsaid element being responsive to the supply of said carrier-waveoscillations from its respective one of said transmission channels toemit corresponding acoustic energy.

10. Echo-ranging apparatus according to claim 9 wherein saidcarrier-wave oscillations are pulsed oscillations, each said elementemitting pulses of acoustic energy alternating with the reception ofechoes.

11. Sonar apparatus comprising: a concave reector having a curved focalsurface, said reector being of circular arc in section; a multiplicityof electromechanical transducers mounted closely side-by-side aroundsaid curved focal surface of the reflector for receiving via the thereflector acoustic echoes from a multiplicity of closelyspaced angulardirections throughout a predetermined angular sector, said transducersbeing mounted in a circular arc concentric with said arc of section toreceive echoes as aforesaid from respective ones of said directions; amultiplicity of reception channels coupled respectively to saidtransducers for detecting echoes received by the transducers; and adisplay unit for providing a display of both direction and range fromwhich echoes detected as aforesaid are received, said display unitincluding means for representing each displayed echo with a direction ofreception in accordance with Whichever of said reception channelsdetects that particular echo.

12. Sonar apparatus according :to claim 11 wherein said directions areequally angularly-spaced from one another throughout said sector.

13. Sonar apparatus comprising: a concave spherical reflector having aspherical focal surface; a multiplicity of electromechanical transducersmounted closely side-byside on said focal surface for receiving via thereflector acoustic echoes from a multiplicity of closely-spaced angulardirections throughout a predetermined angular sector, different ones ofsaid transducers receiving echoes as aforesaid from different ones ofsaid directions; a multiplicity of reception channels coupledrespectively to said transducers for detecting echoes received by thetransducers; and a display unit for providing a display of bothdirection and range from which echoes detected as aforesaid arereceived, said display unit including `means t'or representing eachdisplayed echo with a direction of reception in accordance withwhichever of said reception channels detects that particular echo.

References Cited llJNlTED STATES PATENTS 12,433,332 l2/ 1947 Benioff340-6 X 3,453,502 `l l/ 1948 Dimmick 340-6 X `3,767,386 l0/1956 Ross340-6 2,769,160 i0/ 1956 Fryklund 340-3 2,829,361 4/ 1958 Crandell etal. 340-10 3,001,190 il/1961 Fryklund 340-6 X 3,106,708 i0/ 1963 Sletten343-16 `RICHARD A. FARLEY, Primary Examiner.

